A prior art dive knife has a handle which has an oblong shape and a long recess is formed in the handle. A knife has one end received into the handle and another end thereof is inserted into a cover. The cover is mainly formed by a front cover and a rear cover. The front cover is engaged to the rear cover so as to form as a tightly engaged structure. A lower side of the cover is formed as an opening for receiving the knife. A lower side of the knife is buckled to the cover.
To be safely carried by people, a front end of the knife set has a buckling set. By pressing the buckling set, the knife will release from the cover so that the knife can be taken out from the cover.
However, this prior art structure has only one buckling set which is at a front side of the cover. When sinking into water, since the operation environment is very bad, the buckling set is possible to be pressed by mistake so that the knife will release from the cover to lose in water or even to hurt the diver.